Field of the Invention
The present invention relates to an image processing technique to produce an image of an object lighted by a virtual light source.
Description of the Related Art
A technique to produce (reproduce), from a captured image acquired by image capturing of an actual object under a certain light source environment (light source condition), an object image under a virtually set light source environment by performing image processing such as computer graphics (CG) is called “relighting”.
The image reproduction by the relighting uses physical information on object's shape, reflection characteristic and others.
When the object physical information is unknown, shape information indicating the object's shape is acquired from information on a distance measured using a method such as laser triangulation or a twin-lens stereo method. In addition, the shape information can be acquired, as disclosed in Japanese Patent Laid-Open No. 2010-122158, by a photometric stereo method or the like, as not information indicating a three-dimensional shape but surface normal information indicating surface normals to the object. The reflection characteristic can be acquired from an image produced by image capturing of the object while changing the light source environment and a viewing axis direction. Furthermore, the reflection characteristic is also expressed, in addition to use of the surface normal information, as a model of a Bi-Directional Reflectance Distribution Function (BRDF) or the like.
Japanese Patent Laid-Open No. 2010-231620 discloses a method of editing a three-dimensional CG image. This method sets a reflection region where light is reflected on a three-dimensional model by using three-dimensional shape data and viewpoint data and performs light source setting depending on the reflection region.
However, to set the light source condition, as well as when performing actual image capturing, an editor repeats editing works while changing setting of the light source condition many times until a desired object image is obtained. Such a conventional method of setting the light source condition increases a work load of the editor. Furthermore, it is not realistic to cause an editor unfamiliar with three-dimensional CG image editing works to perform such an editing work.
The method disclosed in Japanese Patent Laid-Open No. 2010-231620 sets the reflection region on the three-dimensional model to reduce the work load in setting the light source condition. However, this method requires a special work for setting the reflection region, which insufficiently reduces the work load in setting the light source condition.